A conventional prior art grill 2 of a type well known in the industry is illustrated in FIG. 1. The prior art grill 2 comprises: a grill housing 4 having an open-topped firebox 5; at least one burner or other heat source 6 which is or will be positioned in a lower portion of the firebox 5; a food support grate 8 positioned within or near an upper portion of the firebox 5 such that the food support grate 8 is above the heat source 6; and a lid 10 having side walls 11 which are rotatably connected to housing side walls 13 extending upwardly from the firebox 5 such that the lid 10 can be pivoted between an open position and a closed position for opening and closing the grill 2.
The heat source 6 used in the grill 2 can be one or more gas burners, one or more electric heating elements, a charcoal bed, a wood pellet burner, or any other type of heat source used in grills or other outdoor cookers. The food support grate 8 can be an open wire convection grate, an infrared cooking grate, a combination convection and infrared grate, or any other type of cooking grate used in grill assemblies or other outdoor cooking apparatuses.
The prior art grill lid 10 illustrated in FIG. 1 has a hood-type configuration which includes a spacious, upwardly-extending interior 12 which (a) provides room for larger food products and (b) can also provide space for one or more warming racks, a rotisserie, and/or other such appliances or features.
The prior art lid 10 further comprises: a horizontally-extending front bottom edge 14 which rests on an upper horizontal front surface 20 of the firebox housing 4 when the lid 10 is closed; a horizontally-extending rear bottom edge 16 positioned on the back side of the grill 2; and an overarching top 18. The overarching top 18 extends (a) upwardly from the horizontally extending rear bottom edge 16 of the lid 10 at the back of the grill 2, then (b) forwardly (and typically also downwardly to some degree as shown in FIG. 1) above the firebox 5 from back to front, and then (c) downwardly to the horizontally extending front bottom edge 14 of the lid 10. The overarching top 18 can be a single-walled structure or can alternatively be a double-walled structure as shown in FIG. 1 in order to reduce the temperature of the outer surface of the lid 10 during operation for greater safety and to protect the lid form discoloration or other damage.
The prior art grill lid 10 is designed such that, when the lid 10 is closed as illustrated in FIG. 1, a horizontal gap 24 is formed across the back side of the grill 2 between the horizontally-extending rear bottom edge 16 of the lid 10 and the horizontally-extending upper edge or end 26 of a short upwardly-extending back wall 28 of the grill housing 4. The horizontal gap 24 between the lid 10 and the back wall 28 of the housing is provided across the back of the prior art grill 10 for venting flue gas from the interior of the grill 2, as illustrated by arrows 30, when the lid 10 is closed.
Conventional prior art grill lids 10 of the type illustrated in FIG. 1 have various significant shortcomings and deficiencies which adversely affect the operation, cooking performance, and thermal efficiency of the prior art cooker 2. During operation, the flue gas 30 produced in the cooker 2 follows the path of least resistance and rushes through the venting gap 24 provided between the back edge 16 of the lid 10 and the back wall 28 of the housing 4. As a result, the volume of flue gas 30 which flows through the front portion 32 of the cooking grate 8 can be much less than the volume which flows through the back portion 34 of grate 8. This results in an uneven heat distribution at the cooking surface which significantly downgrades the cooking performance and the cooking consistency of the prior art grill 2. In addition, the loss of so much unused, high temperature heat energy as a result of the rapid escape of the hot flue gas along path 30 through the gap 24 in the back of the prior art grill 2 greatly reduces the thermal efficiency of the cooking apparatus.
Further, the rush of flue gas along the path of least resistance through the back opening 24 of the prior art grill 2 also creates an undesirable low pressure zone in the front portion of the firebox 5. The creation of this low pressure region further reduces the efficiency of the grill apparatus 2 by (a) pulling an excessive amount of secondary combustion air into the housing firebox 5 and (b) causing the infiltration of additional air through openings which happen to be present in the front of the firebox 5 such as, for example, any gap which is present between the front-side bottom edge 14 of the lid 10 and the upper front surface 20 of the firebox 5. This infiltrating air, particularly if it enters beneath the front edge 14 of the lid 10 at or near the level of the cooking grate, cools the front of the firebox 5, particularly the front portion 32 of the cooking area.
The addition of infiltrating air and/or excessive secondary air also increases the fuel demand of the system in order to heat the additional air to cooking temperature. This, in turn, not only reduces the efficiency of the system, but, by consuming heating capacity, also reduces the maximum cooking temperature achievable in the grill 2.
Also, in the prior art grill 2, the contribution of the prior art lid 10 to the cooking process is very limited. The interior surface 40 of the overarching top 18 of the prior art lid 10 will reflect or emit some radiant energy received from the heat source 6 and/or the cooking grate 8. However, very little heat energy from the hot flue gas is absorbed by the top interior wall 40 of the prior art lid 10 for radiant emission back to the food product. One reason for this is that the flue gas in the upper interior region of the lid 10 is substantially stagnant. Consequently, the high temperature flue gas flows out of the back opening 24 without providing beneficial heat transfer to the top interior wall 40 of the lid 10.
Another problem commonly experienced with the prior art grill lid 10 is that, in windy conditions in excess of 10 miles per hour, wind flow can effectively block the flue gas exhaust opening 24 and/or result in the inflow of outside air through the rear exhaust gap 24 as illustrated in FIG. 2. This disrupts and/or cools the cooking process. Moreover, at increased wind or wind gust velocities, the resulting blockage and/or inflow can create sufficient back pressure within the grill 2 to choke or blow out a grill burner 6, thus stopping the cooking process altogether. When this happens, a dangerous accumulation of uncombusted gas can also occur within the grill 2.